System and method for use of a tunable mass damper to reduce vibrations in wind turbine blades in a locked or idling condition of the rotor hub

ABSTRACT

A system and method are provided for reducing vibrations and loads in one or more rotor blades on a rotor hub of a wind turbine when the rotor hub is in a locked or idling condition. An electronically tunable mass damper is attached to a fixed location on one or more of the rotor blades. The mass damper is maintained on the rotor blades during the locked or idling condition of the rotor hub. The method includes sensing movement of a mass component of the mass damper from vibrations or oscillations induced in the rotor blade. The mass damper is automatically tuned based on the sensed movements of the mass component by automatically varying an electrical characteristic of the mass damper.

FIELD

The present disclosure relates in general to wind turbine powergenerating systems, and more particularly to systems and methods fordamping vibrations and loads in wind turbines, particularly when therotor hub is non-operational in a locked or idling condition.

BACKGROUND

Modern wind turbines are commonly used to supply electricity into theelectrical grid. Wind turbines of this kind generally comprise a towerand a rotor arranged on the tower. The rotor, which typically comprisesa hub and a plurality of blades, is set into rotation under theinfluence of the wind on the blades, wherein the rotation generates atorque that is transmitted through a rotor shaft to a generator, eitherdirectly (“directly driven”) or through the use of a gearbox. This way,the generator produces electricity which can be supplied to theelectrical grid.

There is a trend to make wind turbine blades increasingly longer tocapture more wind and convert the energy of the wind into electricity.This results in the blades being more flexible and more prone toaero-elastic instabilities, e.g., vibrations of the blades that can alsolead to blade oscillations. Vibrating blades create risk of majorpotential damages in the entire wind turbine.

When the wind turbine is in operation, a wind turbine controller mayoperate directly or indirectly any auxiliary drive system such as apitch system or a yaw system to reduce loads on the blades. This way,vibrations of the blades may be counteracted. However, the problem ofaero-elastic instabilities can be serious as well in circumstances whenthe wind turbine is in stand-still conditions, either idling or locked,wherein the blades are susceptible to edgewise oscillations.

At least two types of vibrations may happen during stand-stillconditions. The first one is vortex induced vibration (VIV) at certainangles of attack and may or may not include cross flow vortices shed atfrequencies close to blade eigen frequencies or system frequencies. Thesecond one is stall induced vibration (SIV) when the angle of attack isclose to stall angles and the flow interaction may lead to bladevibrations. The angle of attack may be understood as a geometrical anglebetween a flow direction of the wind and the chord of a rotor blade.There may also be cross flow components to the flow.

The vortex and stall induced vibrations are phenomena that, if notadequately designed or compensated for, can lead to blade failure oraccelerate blade damage.

When the rotor is locked against rotation, for instance due toinstallation, commissioning, or maintenance tasks, the blades canexperience aero-elastic instabilities, such as the VIV and SIVvibrations. Blades are susceptible to these vibrations when angles ofattack are within certain ranges. Because the rotor is locked, rotationof the rotor cannot be used to reduce or damp these vibrations.

A current solution to the cited problems includes the use of aerodynamicdevices attached to the blades to reduce vortices and/or increasedamping. However, this solution may increase costs and time forinstallation and removal of such devices.

Another current practice for wind turbines when not making powerincludes setting the pitch angle of the rotor blades to substantially 90degrees when the rotor is yawed into the wind and prevented fromrotating by means of a locking pin. This particular pitch angle mayreduce loads on the blades, at least with some wind conditions. However,the locking pin may suffer from higher loads when the pitch angle is setat the weathervane position and, even in this position, not allvibrations may be avoided, particularly if the wind direction changesover time.

U.S. Pat. No. 9,316,202 proposes a method and system to guard againstoscillations of the wind turbine blades when the rotor is locked oridling at low speeds that involves attachment of a releasable cover tothe blades that provides a non-aerodynamic surface for a region of theblade. The blade cover is described as a sleeve of a net-like materialthat can be positioned on the blade either before installation or in thefield by service engineers using guidelines.

The present disclosure provides an alternate effective means to reduceor prevent vibrations or oscillations in the wind turbine blades whenthe wind turbine is in a non-operational mode with the rotor hub unableto yaw and locked or idling via use of unique vibration dampers thatwill provide benefits in cost, time and ease of installation, andeffectiveness.

BRIEF DESCRIPTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

The present disclosure encompasses a method for preventing or at leastreducing vibrations and loads in one or more rotor blades on a rotor hubof a wind turbine when the wind turbine is in a non-operational modewith the rotor hub in a locked or idling condition. This mode of thewind turbine may occur, for example during installation, repair,maintenance, disconnection from a grid, or any other scenario that callsfor the rotor hub to be locked against rotation (i.e., at a standstill)or allowed to idle.

The method includes attaching an electronically tunable mass damper at afixed location on one or more of the rotor blades, the mass damperhaving a mass component that moves along a stroke path. The mass damperis maintained on the rotor blades during the locked or idling conditionof the rotor hub. The method includes sensing movement of the masscomponent resulting from vibrations or oscillations induced in the rotorblade during the locked or idling condition. The method thenautomatically tunes the mass damper based on the sensed movement of themass component by varying an electrical characteristic of the massdamper.

In a particular embodiment, the step of automatically tuning the massdamper is accomplished completely by the mass damper without outsideoperator or device action. This embodiment may include adjustingoperating parameters of the tunable mass damper.

The operating conditions or the vibrations or oscillations may be sensedcontinuously or periodically with one or more sensors configured in themass damper.

The method may include tuning the mass damper to an excitation frequencyof the rotor blade during the locked or idling conditions, wherein thisexcitation frequency may change based on a change in the operatingconditions experienced by the rotor blade.

A particular benefit of the mass damper is that it is essentiallyinsensitive to changes in environmental or operating temperature. Theus,the mass damper need not be tuned for temperature.

In a particular embodiment, the mass damper is in communication with aremote central controller (e.g., a wind farm controller), whereinoperating parameters of the mass damper are remotely adjusted by theremote central controller. In this embodiment, the mass damper may alsobe in communication with a mobile smart device that is, in turn, incommunication with the remote central controller. The operator mayadjust the operating parameters of the mass damper via the mobile smartdevice or via the remote central controller.

In another embodiment, each of the rotor blades is configured with oneof the mass dampers, wherein each of the mass dampers is incommunication with a wind turbine controller. In turn, the wind turbinecontroller may be in communication with the remote central controller.

An embodiment of the mass damper includes a flywheel in gearedengagement with a rotation damper, wherein the step of remotely tuningthe mass damper includes electronically controlling a counter-torqueexerted against rotation of the flywheel by the rotation damper.

The flywheel may be in geared engagement with a track gear androtationally driven as the mass component of the mass damper moves alongthe stroke path on the rotor blade, wherein the counter-torque exertedby the rotation damper is proportional to a rotational velocity of theflywheel.

In a particular embodiment, the rotation damper includes an electricalgenerator in geared engagement with and driven by the flywheel, whereinan electrical output of the generator is directly proportional to therotational velocity of the flywheel and is used to produce thecounter-torque. With this embodiment, the tuning process may entailvarying an effective electrical load (i.e., a resistive load) placed onthe generator to change the counter-torque exerted by the generator at agiven rotational speed of the flywheel.

The present invention also encompasses a wind turbine configured forreducing vibrations and loads in rotor blades during a non-operationalmode. The wind turbine includes a plurality of rotor blades on a rotorhub, wherein in the non-operational mode of the wind turbine, the rotorhub is in a locked or idling condition. The wind turbine furtherincludes a mass damper attached at a fixed location on one or more ofthe rotor blades, the mass damper having a mass component that ismovable along a stroke path. One or more sensors configured within themass damper to sense movement of the mass component along the strokepath, wherein the movement is generated by vibrations or oscillationsinduced in the rotor blades during the locked or idling condition of therotor hub; and

wherein the mass damper is automatically tunable by varying anelectrical characteristic of the mass damper based on the sensedmovement of the mass component.

The mass damper may include a dedicated controller in communication witha remote central controller (directly or via the wind turbinecontroller) that controls the tuning process automatically or viaoperator intervention.

The mass damper may also be in communication with a mobile controldevice (e.g., a smart device) that is in communication with the centralcontroller (or the wind turbine controller) for tuning the mass dampervia the mobile control device.

In a particular embodiment, the mass damper includes a flywheelconnected to a rotation damper that exerts a counter-torque againstrotation of the flywheel, wherein the counter-torque is electronicallytunable.

The flywheel may be in geared engagement with a track gear and isrotationally driven as the mass damper moves along a stroke length,wherein the rotation damper comprises an electrical generator in gearedengagement with and driven by the flywheel, wherein an electrical outputof the generator is directly proportional to the rotational velocity ofthe flywheel and produces the counter-torque, the generator coupled to avariable effective resistive load (e.g., an effective resistance) forchanging the generator output.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 illustrates a perspective view of a wind turbine;

FIG. 2 illustrates a simplified view of a wind turbine blade equippedwith a tunable mass damper;

FIG. 3 is a perspective view of a tunable mass damper mounted onto awind turbine blade;

FIG. 4 is a more detailed perspective view of the tunable mass damper ofFIG. 3 ;

FIG. 5 a is a side view of the mass damper of FIG. 4 ;

FIG. 5 b is a bottom view of the mass damper of FIG. 4 ;

FIG. 5 c is a top view of the mass damper of FIG. 4 ;

FIG. 6 is a top diagram view of an alternative embodiment of a tunablemass damper;

FIG. 7 is a control diagram for a tunable mass damper; and

FIG. 8 is a control diagram for a wind turbine utilizing multipletunable mass dampers.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Referring now to the drawings, FIG. 1 illustrates a perspective view ofone embodiment of a wind turbine 10 according to the present disclosure.As shown, the wind turbine 10 generally includes a tower 12 extendingfrom a support surface 14, a nacelle 16 mounted on the tower 12, and arotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatablehub 20 and at least one rotor blade 22 coupled to and extendingoutwardly from the hub 20. For example, in the illustrated embodiment,the rotor 18 includes three rotor blades 22. However, in an alternativeembodiment, the rotor 18 may include more or less than three rotorblades 22. Each rotor blade 22 may be spaced about the hub 20 tofacilitate rotating the rotor 18 to enable kinetic energy to betransferred from the wind into usable mechanical energy, andsubsequently, electrical energy. For instance, the hub 20 may berotatably coupled to an electric generator 24 positioned within thenacelle 16 to permit electrical energy to be produced.

The wind turbine 10 may also include a wind turbine controller 24centralized within the nacelle 16. However, in other embodiments, thecontroller 24 may be located within any other component of the windturbine 10 or at a location outside the wind turbine 10. Further, thecontroller 24 may be communicatively coupled to any number of thecomponents of the wind turbine 10 in order to control the operation ofsuch components and/or implement a corrective or control action. Forexample, the controller 24 may be in communication with individual pitchdrive systems associated with each rotor blade 22 in order to pitch suchblades about a respective pitch axis 28. As such, the controller 24 mayinclude a computer or other suitable processing unit. Thus, in severalembodiments, the controller 24 may include suitable computer-readableinstructions that, when implemented, configure the controller 24 toperform various different functions, such as receiving, transmittingand/or executing wind turbine control signals. Accordingly, thecontroller 24 may generally be configured to control the variousoperating modes (e.g., start-up or shut-down sequences), de-rating orup-rating the wind turbine, and/or individual components of the windturbine 10.

The present disclosure relates to situations wherein the wind turbine 10is non-operational (e.g., not producing electrical power) and the rotor18 (and thus the rotor hub 20) is either locked against rotation or isleft to idle, for instance due to installation, commissioning,maintenance tasks, or any other reason. The controller 24 may remaincommunicatively coupled to at least the pitch drive system in the lockedor idling state of the rotor 18. Alternatively, the “controller”function may also be provided by a separate dedicated controller duringthe locked or idling state of the rotor. This dedicated controller maybe configured to operate autonomously, i.e., independently from the windturbine controller 24, at least in some operating conditions, and may beable to perform tasks such as receiving and emitting signals andprocessing data when the wind turbine controller 24 is otherwiseunavailable.

The wind turbine 10 of FIG. 1 may be placed in an offshore or onshorelocation.

As used herein, the term “controller” refers not only to integratedcircuits referred to in the art as being included in a computer, butalso refers to a microcontroller, a microcomputer, a programmable logiccontroller (PLC), an application specific integrated circuit, and otherprogrammable circuits. The controller is also configured to computeadvanced control algorithms and communicate to a variety of Ethernet orserial-based protocols (Modbus, OPC, CAN, etc.). Additionally, a memorydevice(s) configured with the controller may generally include memoryelement(s) including, but not limited to, computer readable medium(e.g., random access memory (RAM)), computer readable non-volatilemedium (e.g., a flash memory), a floppy disk, a compact disc-read onlymemory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc(DVD) and/or other suitable memory elements. Such memory device(s) maygenerally be configured to store suitable computer-readable instructionsthat, when implemented by the processor(s) 402, configure the controllerto perform the various functions as described herein.

Referring again to FIG. 1 , each of the rotor blades 22 includes a massdamper 44 in accordance with aspects of this disclosure mounted thereon,for example at a fixed location that is closer to the blade tip ratherthan the blade root.

FIG. 2 is a diagram view of a conventional rotor blade 22 that includesan opposite blade root 30, leading edge 36, trailing edge 38, suctionside 42, and pressure side 40. The chord-wise dimension 34 of the blade22 is also indicated. The mass damper 44 is mounted chord-wise onto thesuction side 42 of the blade 22 generally adjacent to the blade tip 32.The mass damper could just as well be mounted onto the suction side 42of the rotor blade 22. The mass damper 44 is explained in greater detailbelow.

FIG. 3 is a perspective external view of the mass damper 44 on the rotorblade 22, and particularly illustrates an embodiment of an attachingsystem 45 for fixing the mass damper on the blade. The attaching systemincludes opposite clamping shells 46 that conform to the blade's outerpressure side surface 40 and suction side surface 42. The clampingshells 46 extend across the chord-wise width of the rotor blade 22 andinclude a leading-edge flange 48 and a trailing edge flange 50. The massdamper 44 includes a base 56 that extends above one of the clampingshells 46 between the flanges 48, 50. The base 56 is bolted to theflanges with bolts 52, wherein the bolts 52 also serve to bolt theopposite flanges 48 together as well as the opposite flanges 50.

It should be appreciated that the mass damper 44 may be mounted to therotor blade using any suitable nonpermanent attaching system, includingmechanical fasteners, adhesives, inflatable devices, and so forth.

The mass damper 44 includes a housing 54 mounted onto the base 56,wherein the working components of the mass damper 44 are containedwithin the housing 54, as described in greater detail below. The housing56 includes side walls 68, end walls 70, and a top 60. It should beappreciated that the housing 56 may have any geometric shape.

Referring to the perspective view of FIG. 4 and the various views ofFIGS. 5 a-5 c and 6, an embodiment of a mass damper 44 in accordancewith aspects of the invention is provided. The mass damper 44 isconfigured to reduce vibrations and loads in rotor blades during anon-operational mode of the wind turbine wherein the rotor hub in alocked or idling condition. The mass damper 44 is mounted to at leastone, and preferably all, of the rotor blades (as discussed above) beforeor shortly after placing the wind turbine in the non-operational mode orduring installation of the wind turbine. The mass damper 44 is tunableto an excitation frequency of the respective rotor blade or systemfrequencies as operating conditions experienced by the wind turbinechange during the locked or idling condition, as explained in greaterdetail below.

The mass damper 44 includes a mass component 47 that moves along astroke path within the mass damper 44. The term “mass component” is usedherein to collectively refer to a mass of the totality of the componentson a frame 72 (and is inclusive of the frame 72) that move along a track64 within the mass damper 44, as described in more detail below.

The illustrated embodiment of the mass damper 44 includes a flywheel 74that is in geared engagement with a rotation damper 80. The mass damperis tuned by controlling and changing a counter-torque exerted againstrotation of the flywheel 74 by the rotation damper 80. This tuningfunction is accomplished automatically and wholly by the mass damper 44via an internal electronic controller 100 (FIG. 6 ) at any time the massdamper 44 is mounted to a rotor blade 22. Thus, as environmental oroperating conditions experienced by the wind turbine change during thenon-operational mode resulting in a change in vibrations or oscillationsinduced in the blades, the mass damper 44 is effectively andautomatically tuned to the change in the vibrations or oscillations.

The flywheel 74 is rotationally configured on a frame 72 that moveslinearly along the chord-wise stroke path within the housing 54 relativeto the rotor blade 22. The flywheel 74 is coupled to a shaft 76 that issupported for rotation by bearings 88. The flywheel 74 is in gearedengagement with the first track gear 64 that may be mounted to the base56, as particularly seen in FIG. 4 . The track gear 64 extendslongitudinally along the base 56 and effectively defines a length of thestroke path within the mass damper 44. The flywheel 74 has a gearedouter circumferential surface 78 that meshes with the track gear 64.Thus, edge-wise vibrations or oscillations induced in the rotor bladecause the flywheel 74 (and mass component 47) to rotate and movelinearly back-and-forth along the track gear 64. The mass damper 44 isautomatically tuned by increasing or decreasing a counter-torque appliedto the flywheel 74, as described below.

Although not illustrated in the figures, the flywheel 74 may also be ingeared engagement with a second track gear mounted to an underside ofthe top 60 of the housing 54.

In the depicted embodiment, the flywheel 74 is geared directly to thetrack gear 64 (which may include an additional upper track gear). Itshould be appreciated that an intermediate gear may be used between theflywheel 74 and the track gear 64.

In addition to the weight of the components on (and including) the frame72, the mass component 47 may also include additional ballast weights 93that can be added to or removed from the frame 72, as depicted in theembodiment of FIG. 6 .

As mentioned, the frame 72 (with components fixed thereon) is movablealong the track gear 64 (which may include an additional upper housinggear) within the housing 54. For this, the frame 72 may include a numberof rollers 86 fixed thereto that ride along bottom runners 58 mounted on(or formed integral with) the base 56 and top runners 62 supported by orformed on the top 60 of the housing 56. Side rollers 87 may be mountedon the frame 72 to roll along the side walls 68 of the housing 54. Thus,the frame 72 may be supported for direct rolling engagement with thehousing 54 and base 56 via the rollers 86, 87.

Oppositely-acting torsion springs 90 are provided to oppose theback-and-forth motion of the frame 72 (and attached components) relativeto the track gears 64, 66, which also results in dampening of the bladevibrations and oscillations. One end of each spring 90 is fixed to theframe 72 and the other end of the spring 90 is fixed to the shaft 76.Thus, as the shaft 76 rotates in either direction, it “tightens” one ofthe torsion springs 90 to generate an opposing force against rotationsof the shaft 76 (and thus rotation of the flywheel 74 fixed to the shaft76).

The rotation damper 80 is mounted on the frame 72 and is in gearedengagement (direct or indirect) with the flywheel 74. For example, therotation damper may be in direct geared engagement with the outercircumferential surface 78 of the flywheel 74. The rotation damper 80 is“rotational” in that it is rotationally driven and produces acounter-torque that opposes rotation of the flywheel 74, thiscounter-torque being proportional to rotational velocity of the flywheel74.

In a particular embodiment depicted in the figures, the rotation damper80 includes at least one electrical generator 82 in geared engagementwith (direct or indirect) and driven by the flywheel 74. In the depictedembodiment, the generator 82 is driven by a gear 84 that is also inengagement with the outer circumferential surface 78 of the flywheel 74.Thus, the generator 82 produces an electrical output (i.e., a current)that is directly proportional to the rotational velocity of the flywheel74. The electrical output produces the counter-torque and, thus, thecounter-torque is directly proportional to the rotational velocity ofthe flywheel 74.

It is a characteristic of electric generators that current from thegenerator produces a reaction torque (counter-torque) that, at a givenload on the generator, is proportional to the magnitude of the current.Torque control of the generator works by changing the effectiveresistive load placed on the generator. This principle is utilized inthe present invention to provide a remote electrical tuning capabilityto the mass damper 44.

Thus, by changing the effective resistive load on the generator 82 feltacross the generator terminals, current (and thus counter-torque)produced by the generator 82 at a given rotational velocity of theflywheel 74 can be varied. A lower effective resistance leads to morecurrent and more counter-torque, thus more damping capability of themass damper 44. Controlling the effective resistance of the generatorload effectively and automatically tunes the damping of the mass damper44. Embodiments for varying the effective resistive load on thegenerator are discussed below with reference to FIG. 7 .

In the embodiment of the mass damper 44 depicted in FIGS. 4 and 5 a-5 c,a single generator 82 is utilized to provide the tunable dampingcapability. It should be appreciated that that a plurality of generators82 may be utilized to achieve a desired tuning capability within theconstraints of available space on the frame 72. For example, in theembodiment depicted in FIG. 6 , two generators 82 are engaged with theflywheel 74, with both generators 82 in communication with a commoncontroller 100.

Referring to FIG. 6 , the mass damper 44 (in particular, the masscomponent 47) has an effective stroke length in the chord-wise directionacross the blade, wherein blade vibrations or oscillations of relativelylower amplitude result in a shorter stroke (shorter path of travel ofthe frame 72 on the track gear 64) and vibrations or oscillations ofrelatively greater amplitude result in a longer stroke of the masscomponent 47. Tuning the mass damper 44 to the stroke length isaccomplished by changing the effective resistive load on the generator,as discussed above. Tuning of the device to limit the travel (i.e.,stroke length) at higher vibration/oscillation amplitudes is animportant safety feature so that travel of the mass component 47 doesnot exceed the available stroke path/length defined within the massdamper 44. On the other hand, it is desirable to tune the mass damper 44to maximize its performance at lower amplitudes. Thus, the tuning schemeaims to increase stroke at lower amplitudes to maximize performance ofthe device, while limiting stroke at higher amplitudes to avoid damageto the mass damper 44. Thus, depending on the amplitude of thevibrations/oscillations induced in the rotor blade by the operatingconditions experienced by the wind turbine, a desired stroke length isset or defined for the mass damper 44 to reduce the amplitude.

The mass damper 44 includes a dedicated onboard controller 100 to adjustor change the effective resistive load placed on the generator 82,thereby tuning the mass damper. Referring to FIG. 6 , a sensor array 92is provided on the frame 72 and is in communication with the controller100. This array 92 may include one or more sensors. In a particularembodiment, three local sensors are configured in the array 92.

The first local sensor in the array 92 may be a position sensorconfigured to sense the instantaneous position of the mass component 47along the track 64 to determine the current operating state of the massdamper 44. This is the main sensor used to provide feedback for thecontroller 100 to adjust the effective resistance on the generator. Thisfirst sensor may be, for example an incremental rotary encoder.

The second local sensor in the array 92 may be a neutral position sensorconfigured to provide a pulse (or other indication) at the neutralposition of the mass component 47 corresponding to the middle of thestroke path. This sensor may be used as a check to ensure that the firstsensor (e.g., encoder) is aligned correctly. If the encoder does notagree with the neutral position sensor, the encoder is reset to ensure acorrect neutral position. This second sensor may be, for example, aninductive or hall effect sensor on the moving frame 72, and a magnet onthe base 56. When the sensor travels over the magnet, a pulse isgenerated.

The third local sensor in the array 92 may be a limit position sensor,such as an inductive/hall effect sensor. This sensor is located on themass component 47 (e.g., on the frame 72) in a way that does not respondto the neutral position sensor. The magnets for this third sensor areplaced at the limits of the stroke path/length. If a pulse is detectedfrom this sensor, action is taken to maximize the generator torque tooppose the motion because the moving frame is in danger of exceeding itsdesign stroke.

FIG. 7 is a simplified circuit diagram that depicts control aspects ofthe rotation damper 80, particularly the generator 82. The generator 82is engaged with the flywheel 74 via the gear 84. An effective resistiveload 108 is selectively placed across the generator 82 and controlled bythe controller 100 (which may be a conventional PID controller).

In one embodiment, a circuit is established across the generatorterminals. The circuit includes a resistive load 108 (which may befixed/non-variable). A relay 104 is used to alternately place/removethis resistor 108 from the circuit. When the resistor 108 is placedacross the generator terminals, the generator 82 produces an outputcurrent, which results in the counter-torque discussed above. Thiscounter-torque is proportional to the generator output (current). Apulse width modulation (PWM) module 110 is used to alternately open andclose the relay 104. The controller 100 adjusts the duty cycle of thePWM module 110 to control the amount of time the resistor 108 is placedin the circuit. Thus, an increased duty cycle (frequency) of the relay104 results in an increase of the generator output and, thus, anincrease in the counter-torque applied to the flywheel. Even though theresistor 108 may have a fixed resistance value, the effective resistanceseen by the generator is varied by changing the duty cycle of the PWMmodule 110.

In an alternate embodiment, the resistive load 108 may be a variableload, such as a variable resistor indicated by the arrow in FIG. 7 or aresistor branch circuit wherein multiple resistors are variably combinedto change the effective resistive value placed on the generator 82. ThePID controller 100 may directly control the rheostat or resistor branchcircuit to change the effective resistive load 108 placed on thegenerator 82 by altering the actual resistive value of the load 108.

The controller 100 receives position data via the sensor array 92 andcontrols the effective resistive load 108 (by controlling the variableresistor or the duty cycle of the PWM) in an open or closed feedbackloop to control the counter-torque produced by the generator 82 as afunction of stroke length of the mass component 47.

The circuit across the generator 82 may include a bypass relay 103controlled by the controller 100 for relatively infrequent low voltageoperation when maximum counter-torque is required.

Still referring to FIG. 7 , as mentioned, the controller 100 may be anindividual dedicated controller configured within the housing 54 foreach individual mass damper 44. The controller 100 may have a dedicatedpower supply, such as a rechargeable battery 102, or in an alternateembodiment may be supplied with power from a source in the wind turbine.

The controller 100 may be in communication with a remotely locatedcentral controller 112 (directly or via the wind turbine controller 24)for receipt or exchange of control commands or data therewith. Forexample, the central controller 112 may generate control commands tochange certain operating parameters of the mass damper 44, such as thestroke length, response characteristics of the mass damper, power modes,duty cycle of the PWM, etc. The controller 100 may be in communicationwith a mobile hand-held controller 116 (e.g., a mobile smart device)directly or via an intermediary controller. The mobile controller 116may run an application that allows an operator to monitor operation ofthe mass damper 44 and/or control the operating parameters thereof. Inthe depicted embodiment, the mobile controller 116 and the centralcontroller 112 may be in direct communication with the mass dampercontroller 100 via a wireless network 120. The mass damper 44 would, inthis case, also include wireless transmission and reception capability.

FIG. 8 depicts a control scheme wherein each rotor blade 22 of the windturbine has one of the mass dampers 44 mounted thereon. Each damper 44may have its own dedicated controller 100 in communication with the windturbine controller 24 via a wireless network 121 or a wired connection.The wind turbine controller 24 may, in turn, be in communication withthe central controller 112 via a wireless network 118. The mobile smartdevice 116 may be in direct communication with the wind turbinecontroller 24 or via the central controller 112 (and wireless network120).

It should be appreciated that various control schemes and architecturemay be utilized to provide the automatic tuning capability for the massdampers 44 on the rotor blades 22 and remote adjustment or monitoring ofthe operating state or parameters of the mass dampers 44.

In certain embodiments, one or more sensors 95, 115 located on theblades 22 or other static locations of the wind turbine may be utilizedto provide data indicative of vibrations or oscillations induced in therotor blades during the locked or idling state of the rotor 18. Theoscillations or vibrations may be detected or measured directly bydisplacement sensors 95 (e.g., accelerometers or strain gauges) locateddirectly on the rotor blades. A vibration of a blade may be determinedwhen the strain or deformation parameter satisfies a strain ordeformation threshold, which may be determined by the controller 100 (orany of the other controllers 112, 116).

The sensors 95, 115 may be in communication with the central controller112 directly or via the wind turbine controller 24, as depicted in FIGS.7 and 8 . In order to conserve the internal power supply (e.g., battery102) in the mass dampers 44, it may be desired that the devices 44 areplaced in a low-power sleep mode until the vibrations or oscillationsinduced in the blades reaches a threshold level as determined by thecentral controller 112 based on the data from the sensors 95, 115. Oncethis threshold is met, the central controller 112 may issue a “turn on”command to the mass dampers 44 directly or via the wind turbinecontroller 24.

Alternatively, the oscillations or vibrations may be predicted orinferred based on data from sensors disposed on the wind turbine tomeasure wind speed, wind direction, yaw position of the rotor hub, etc.For this, the wind turbine may include one or more wind parametersensors 115 (FIG. 1 ) for measuring various wind parameters upwind ofthe wind turbine. The actual wind parameter(s) may be any one orcombination of the following: wind gust, wind speed, wind direction,wind acceleration, wind turbulence, wind shear, wind veer, wake, windup-flow, or similar. Further, the one or more sensors 115 may include atleast one LIDAR sensor for measuring upwind parameters. The LIDARsensors may be located on the wind turbine tower 12, on one or more ofthe wind turbine blades 22, on the nacelle 16, one a meteorological mastof the wind turbine, or at any other suitable location. In still furtherembodiments, the wind parameter sensor 115 may be located in anysuitable location near the wind turbine 10. The sensors 115 may beconfigured to measure a wind parameter ahead of at least one specificportion, typically the most significant sections of the blades 22 interms of contributions of those sections to aerodynamic torque on theblades 22. These sections may include, for example, sections close tothe tip of the blade.

Further aspects of the invention are provided by the subject matter ofthe following clauses:

Clause 1. A method for reducing vibrations and loads in one or morerotor blades on a rotor hub of a wind turbine when the rotor hub is in alocked or idling condition, the method comprising: attaching anelectronically tunable mass damper at fixed location on one or more ofthe rotor blades, the tunable mass damper having a mass component thatmoves along a stroke path; maintaining the mass damper on the rotorblades during the locked or idling condition of the rotor hub; sensingmovement of the mass component resulting from vibrations or oscillationsinduced in the rotor blade during the locked or idling condition; andautomatically tuning the mass damper based on the sensed movement of themass component by varying an electrical characteristic of the massdamper.

Clause 2. The method according to clause 1, wherein the step ofautomatically tuning the mass damper is accomplished completely by themass damper without outside operator or device action.

Clause 3. The method according to any one of clauses 1-2, furthercomprising automatically and remotely adjusting operating parameters ofthe tunable mass damper.

Clause 4. The method according to any one of clauses 1-3, wherein themovement of the mass component is sensed continuously or periodicallywith one or more sensors configured in the mass damper.

Clause 5. The method according to any one of clauses 1-4, wherein themass damper is tuned to an excitation frequency of the rotor bladeduring the locked or idling conditions.

Clause 6. The method according to any one of clauses 1-5, wherein themass damper is operationally insensitive to temperature changes.

Clause 7. The method according to any one of clauses 1-6, wherein themass damper is in communication with a remote central controller,wherein operating parameters of the mass damper are remotely adjusted bythe remote central controller.

Clause 8. The method according to any one of clauses 1-7, wherein themass damper is also in communication with a mobile smart device that isin communication with the remote central controller.

Clause 9. The method according to any one of clauses 1-8, wherein anoperator adjusts the operating parameters of the mass damper via themobile smart device or via the remote central controller.

Clause 10. The method according to any one of clauses 1-9, wherein eachof the rotor blades is configured with one of the mass dampers, each ofthe mass dampers in communication with a wind turbine controller, thewind turbine controller in communication with the remote centralcontroller.

Clause 11. The method according to any one of clauses 1-10, wherein themass damper includes a flywheel connected to a rotation damper, the stepof automatically tuning the mass damper comprising electronicallycontrolling a counter-torque exerted against rotation of the flywheel bythe rotation damper.

Clause 12. The method according to any one of clauses 1-11, wherein theflywheel is in geared engagement with a track gear and is rotationallydriven as the mass component moves along the stroke path, the flywheelcoupled to a shaft that is coupled to the rotation damper, wherein thecounter-torque exerted by the rotation damper is proportional to arotational velocity of the flywheel.

Clause 13. The method according to any one of clauses 1-12, wherein therotation damper includes an electrical generator in geared engagementwith and driven by the flywheel, wherein an electrical output of thegenerator is directly proportional to the rotational velocity of theflywheel and is used to produce the counter-torque.

Clause 14. The method according to any one of clauses 1-3, wherein theautomatic tuning step comprises remotely varying an effective resistanceplaced on the generator to change the counter-torque exerted by thegenerator at a given rotational speed of the flywheel.

Clause 15. A wind turbine configured for reducing vibrations and loadsin rotor blades during a non-operational mode of the wind turbine,comprising: a plurality of rotor blades on a rotor hub; in thenon-operational mode of the wind turbine with the rotor hub in a lockedor idling condition, the wind turbine further comprising a mass damperattached at a fixed location on one or more of the rotor blades, themass damper comprising a mass component that is movable along a strokepath; one or more sensors configured within the mass damper to sensemovement of the mass component along the stroke path, wherein themovement is generated by vibrations or oscillations induced in the rotorblades during the locked or idling condition of the rotor hub; andwherein the mass damper is automatically tunable by varying anelectrical characteristic of the mass damper based on the sensedmovement of the mass component.

Clause 16. The wind turbine according to clause 15, wherein the massdamper is in communication with a remote central controller, whereinoperating parameters of the mass damper are remotely adjusted by theremote central controller.

Clause 17. The wind turbine according to any one of clauses 15-16,wherein the mass damper is also in communication with a mobile smartdevice, wherein an operator adjusts the operating parameters of the massdamper via the mobile smart device or via the remote central controller.

Clause 18. The wind turbine according to any one of clauses 15-17,wherein each of the rotor blades is configured with one of the massdampers, each of the mass dampers in communication with a wind turbinecontroller, the wind turbine controller in communication with the remotecentral controller.

Clause 19. The wind turbine according to any one of clauses 15-18,wherein the mass damper comprises a flywheel connected to a rotationdamper that exerts a counter-torque against rotation of the flywheel,wherein the counter-torque is electronically tunable.

Clause 20. The wind turbine according to any one of clauses 15-19,wherein the flywheel is in geared engagement with a track gear and isrotationally driven as the mass damper moves along a stroke length,wherein the rotation damper comprises an electrical generator in gearedengagement with and driven by the flywheel, wherein an electrical outputof the generator is directly proportional to the rotational velocity ofthe flywheel and produces the counter-torque, the generator coupled to avariable effective resistive load for changing the generator output.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A method for reducing vibrations and loads in oneor more rotor blades on a rotor hub of a wind turbine when the rotor hubis in a locked or idling condition, the method comprising: attaching anelectronically tunable mass damper at a fixed location on one or more ofthe rotor blades, the tunable mass damper having a mass component thatmoves along a stroke path; maintaining the mass damper on the rotorblades during the locked or idling condition of the rotor hub; sensingmovement of the mass component resulting from vibrations or oscillationsinduced in the rotor blade during the locked or idling condition; andautomatically tuning the mass damper based on the sensed movement of themass component by varying an electrical characteristic of the massdamper.
 2. The method according to claim 1, wherein the step ofautomatically tuning the mass damper is accomplished completely by themass damper without outside operator or device action.
 3. The methodaccording to claim 2, further comprising automatically and remotelyadjusting operating parameters of the tunable mass damper.
 4. The methodaccording to claim 1, wherein the movement of the mass component issensed continuously or periodically with one or more sensors configuredin the mass damper.
 5. The method according to claim 1, wherein the massdamper is tuned to an excitation frequency of the rotor blade during thelocked or idling conditions.
 6. The method according to claim 1, whereinthe mass damper is operationally insensitive to temperature changes. 7.The method according to claim 1, wherein the mass damper is incommunication with a remote central controller, wherein operatingparameters of the mass damper are remotely adjusted by the remotecentral controller.
 8. The method according to claim 7, wherein the massdamper is also in communication with a mobile smart device that is incommunication with the remote central controller.
 9. The methodaccording to claim 8, wherein an operator adjusts the operatingparameters of the mass damper via the mobile smart device or via theremote central controller.
 10. The method according to claim 7, whereineach of the rotor blades is configured with one of the mass dampers,each of the mass dampers in communication with a wind turbinecontroller, the wind turbine controller in communication with the remotecentral controller.
 11. The method according to claim 1, wherein themass damper includes a flywheel connected to a rotation damper, the stepof automatically tuning the mass damper comprising electronicallycontrolling a counter-torque exerted against rotation of the flywheel bythe rotation damper.
 12. The method according to claim 11, wherein theflywheel is in geared engagement with a track gear and is rotationallydriven as the mass component moves along the stroke path, the flywheelcoupled to a shaft that is coupled to the rotation damper, wherein thecounter-torque exerted by the rotation damper is proportional to arotational velocity of the flywheel.
 13. The method according to claim12, wherein the rotation damper includes an electrical generator ingeared engagement with and driven by the flywheel, wherein an electricaloutput of the generator is directly proportional to the rotationalvelocity of the flywheel and is used to produce the counter-torque. 14.The method according to claim 13, wherein the automatic tuning stepcomprises remotely varying an effective resistance placed on thegenerator to change the counter-torque exerted by the generator at agiven rotational speed of the flywheel.
 15. A wind turbine configuredfor reducing vibrations and loads in rotor blades during anon-operational mode of the wind turbine, comprising: a plurality ofrotor blades on a rotor hub; in the non-operational mode of the windturbine with the rotor hub in a locked or idling condition, the windturbine further comprising a mass damper attached at a fixed location onone or more of the rotor blades, the mass damper comprising a masscomponent that is movable along a stroke path; one or more sensorsconfigured within the mass damper to sense movement of the masscomponent along the stroke path, wherein the movement is generated byvibrations or oscillations induced in the rotor blades during the lockedor idling condition of the rotor hub; and wherein the mass damper isautomatically tunable by varying an electrical characteristic of themass damper based on the sensed movement of the mass component.
 16. Thewind turbine according to claim 15, wherein the mass damper is incommunication with a remote central controller, wherein operatingparameters of the mass damper are remotely adjusted by the remotecentral controller.
 17. The wind turbine according to claim 16, whereinthe mass damper is also in communication with a mobile smart device,wherein an operator adjusts the operating parameters of the mass dampervia the mobile smart device or via the remote central controller. 18.The wind turbine according to claim 16, wherein each of the rotor bladesis configured with one of the mass dampers, each of the mass dampers incommunication with a wind turbine controller, the wind turbinecontroller in communication with the remote central controller.
 19. Thewind turbine according to claim 15, wherein the mass damper comprises aflywheel connected to a rotation damper that exerts a counter-torqueagainst rotation of the flywheel, wherein the counter-torque iselectronically tunable.
 20. The wind turbine according to claim 19,wherein the flywheel is in geared engagement with a track gear and isrotationally driven as the mass damper moves along a stroke length,wherein the rotation damper comprises an electrical generator in gearedengagement with and driven by the flywheel, wherein an electrical outputof the generator is directly proportional to the rotational velocity ofthe flywheel and produces the counter-torque, the generator coupled to avariable effective resistive load for changing the generator output.